1. Field of Invention
The present invention relates in general to a color filter of a display, and more particularly, to a color filter of a liquid crystal display that has a black matrix (BM).
2. Related Art
The liquid crystal display panel is operative to generate color images by using three colors (red, green and blue) photoresist patterns. Currently, the main stream for fabricating the color filter includes color distribution method involved with the black matrix technique and RGB color photoresist technique. The conventional black matrix technique sputters a chromium (Cr) or a chromium oxide metal film on a glass substrate. By applying exposure, development and etching processes, the black matrix is formed, followed by the RGB color photoresist technique. The color photoresist technique uses exposure and development to a color photoressist pattern in the opening of the black matrix. Thereby, the adjacent photoresist patterns of red (R), green (G) and blue (B) are isolated by black matrix, such that the color contrast for display is improved, while the impurity of color light is avoided.
In recent year, resin has been used to replace chromium for forming black matrix due to the environment consideration. The resin is typically mixed with carbon. The applicable black matrix array does not only resolve the pollution caused by forming the metal black matrix, but also reduce reflection and promote color contrast to have better color performance. However, the resin black matrix has a relative lower optical density (OD) compared to the same thickness of metal black matrix. Therefore, the light shielding effect of the metal black matrix is much superior to that of the resin black matrix. Typically, the required optical density of a color filter has to be over 4.0, which for the chromium black matrix to achieve needs only 0.15 microns in thickness, while the resin black matrix needs more than 1.1 microns. With regard to the liquid crystal display television products that have brightness requirement, the optical density has to be over 4.5 to completely shield the light source. Such requirement of optical density ultimately increases the thickness of the resin black matrix up to 1.3 microns. When the optical density is achieved simply by increasing the thickness of the resin black matrix, the overlap between the black matrix and the color photoresist patterns protrude significantly to degrade the planarity of the substrate layers. Therefore, the thickness uniformity cannot be obtained to cause abnormal orientation of liquid crystal molecules.